MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Contact: JPL/Alan Buis (818) 354-0474 March 17, 2002
NASA Headquarters/David E. Steitz (202) 358-1730
NASA Goddard Space Flight Center/Lynn Chandler (301) 286-2806
German Center for Air and Space Flight/Vanadis Weber
+49 (0) 2203/601-3068
University of Texas Center for Space Research/Margaret Baguio
(512) 471-6922
SCIENTISTS SAY "GRACE" AS WATER-SENSING SATELLITES LIFT OFF
NASA and the German Center for Air and Space Flight today
successfully launched the Gravity Recovery and Climate
Experiment, or "Grace," mission into Earth orbit at 1:21:27
a.m. Pacific time from Russia's Plesetsk Cosmodrome. The
mission, comprised of identical twin satellites, will
precisely measure Earth's shifting water masses and map their
effects on Earth's gravity field.
The five-year Grace mission -- the first launch of NASA's
Earth System Science Pathfinder program -- will be a scientific
boon to researchers who study Earth with space-based
instruments. The monthly gravity maps generated by Grace will
be up to 1,000 times more accurate than those currently in
use, substantially improving the accuracy of many techniques
used by oceanographers, hydrologists, glaciologists,
geologists and other scientists to study phenomena that
influence climate. These phenomena range from shallow and
deep ocean currents, water movement on and beneath Earth's
surface, and the movement and changing mass of ice sheets, to
sea-level heights, sea-level rise and changes in the structure
of the solid Earth.
Under partly cloudy, cold skies, the Grace twins lifted
off on a Russian Rockot launch vehicle. Riding nearly 160,000
kilograms (approximately 350,000 pounds) of thrust, the rocket
headed northward over the Arctic Ocean and Alaska, then south
across the Pacific Ocean and Antarctica before heading north
again over Africa and Europe. At 85 minutes, 38 seconds into
the mission -- or 2:47 a.m. Pacific time -- the satellites separated
from the launch vehicle's third stage above Africa into a
polar orbit 500 kilometers (311 miles) above Earth.
Ground controllers successfully acquired the spacecraft's
signal from the German Space Operations Center's ground
tracking station in Weilheim, Germany at 2:49 a.m. Pacific
time. Initial telemetry reports received by the Grace team
show both satellites to be in excellent health.
Following separation, the leading Grace satellite began
pulling away from the trailing satellite at a relative speed
of about 0.5 meters (1.6 feet) per second. Over the course of
the next four days, the satellites will be spaced 220
kilometers (137 miles) apart -- a little more than the distance
between Los Angeles and San Diego.
As they race around the globe 16 times a day, the
satellites will sense minute variations in Earth's surface
mass below and corresponding variations in Earth's
gravitational pull. Regions of slightly stronger gravity will
affect the lead satellite first, pulling it slightly away from
the trailing satellite. By measuring the constantly changing
distance between the two satellites using an extremely
sensitive microwave ranging system and combining that data
with precise positioning measurements from Global Positioning
System instruments, scientists will be able to construct a
precise Earth gravity map.
During the next two and a half weeks, basic satellite
operations will be established. During a subsequent three-
week commissioning phase, Grace's science instruments and
supporting systems will be powered up, evaluated and
calibrated. The performance of the Grace system for measuring
Earth gravity will then be validated over the following six
months. The mission then enters its observational phase,
during which routine operational data products will be made
available to scientists.
Additional information about the Grace program is
available on the Internet at:
http://www.csr.utexas.edu/grace .
Grace is a joint partnership between NASA and the German
Center for Air and Space Flight (Deutsches Zentrum fur Luft
und Rumfahrt, or DLR). NASA's Jet Propulsion Laboratory,
Pasadena, Calif., manages the U.S. portion of the project for
NASA's Office of Earth Science, Washington. Science data
processing, distribution, archiving and product verification
are managed under a cooperative arrangement between JPL and
the University of Texas' Austin-based Center for Space
Research in the United States and Germany's Earth Research
Center (or GeoForschungsZentrum).
JPL is a division of the California Institute of
Technology in Pasadena.
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